Ana BANICA Prøveforelesning 2006 1 Analytical methods for studying trace metal speciation in the natural environment (Analytiske metoder for speciering

Ana BANICA Prøveforelesning 2006

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Analytical methods for studying trace metal speciation

in the natural environment

(Analytiske metoder for speciering av spormetaller i naturen)

As Hg Cr Sn Se Pb Cd Fe Cu Zn Ni Co Al …..

Date: 8 February 2006Duration: 45 minutesTarget groups: 1st and 2nd year Chemistry students


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Contents

1. Chemical speciation and fractionation

2. Analytical strategies and methodological approaches

3. In-situ (on-field) speciation analysis in aquatic systems

4. Conclusions


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1.

Chemical Speciation and Fractionation


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Chemical Speciation and Fractionation

• Chemical species• Speciation analysis• Speciation of an element• Fractionation

Acc. to “Guidelines for terms related to chemical speciation and fractionation of elements. Definitions, structural aspects, and methodological approaches” (IUPAC Recommendations, Pure Appl. Chem. 2000)

- Specific forms of an element

Fe(II)/Fe(III); As(III)/As(V)

CuCl2/CuCO3; Hg/CH3HgCl

- Activity of identifying and measuring species

- Distribution amongst chemical species in a system- Analytes classification according

to physical or chemical properties


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Speciation of Metals

• Isotopic composition• Electronic and oxidation state• Inorganic compounds and complexes• Organometalic compounds• Organic and macromolecular complexes


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Benefits and Fields of Interest


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What is determining the biogeochemical impact of the metal ions species in aqueous systems?

• Concentration• Nature of considered organism• Physico-chemical form:

• Particulate ( > 1 µm)• Colloidal (1 nm – 1 µm)• Dissolved (< 1 nm):

Free metal ions Simple inorganic complexes Complexes with anthropogenic and natural

ligands


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2.

Analytical Strategies

and Methodological Approaches


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Analytical Strategy – the Main Steps

1. Formulation of the problem

2. Sampling and sample preparation

3. Measurement of the analytical signal

4. Analytical signal interpretation (quantitative and qualitative)

5. Critical evaluation of the analytical performances and method validation


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What is relevant in a metal speciation study?

Individual speciesGroups

of different species with similar properties

1.Formulation of the problem


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• Exchangeable fraction: species most available for bio-uptake (reagent used: acetic acid 0.11 M)

• Reducible fraction: potentially available for plants (reagent used: a reducing agent like hydroxylamine chloride)

• Oxidizable fraction: potentially available for plants (reagent used: an oxidizing agent like H2O2 and NH4COOCH3)

• Rezidual fraction: contains naturally occurring minerals

Bio-uptake of Metal Species in Soils


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Bio-uptake of Metal Species in Aquatic Systems

• Free metal ions – related to biological uptake

• Dynamic metal species (free metal ions and small

labile complexes) – potentially availably for organisms

• The particulate and colloidal species – role in

transport and residence time

The total extractable metals – the reservoir of metal in the test solution


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The Baia Mare Accident

!! Higher toxicity due to heavy metals (Cu(II),

Zn(II))

Surface-water sampling sites


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Metal Species in Aquatic Systems

• Free metal ions – related to biological uptake

• Dynamic metal species (free metal ions and small

labile complexes) – potentially availably for organisms

• The particulate and colloidal species – role in

transport and residence time

The total extractable metals – the reservoir of metal in the test solution


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A major challenge in speciation analysis

Sampling – Sample preparation

SamplingTransportPre-treatmentPreservation

Contamination

Loss of analyte

Species transformation

2. Sampling and Sample Preparation


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What is influencing the species stability?

• Chemical factors

• Physical factors

• Biological factors


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Treatments for Sample Preservation

• Acidification• Low-temperature• Drying• Freezing• Pasteurization• Lyophilization• Adsorption on cartridges or

solid-phase micro-columns• Storage in the dark

Preservation of Sb samples:

- Acidification to prevent hydrolysis

- Extraction on solid-phase


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Artifacts in Sample Speciation

O2Fe(OH)3

• Precipitation• Sorption onto the container walls

Fe2+

0 4 8 12 16 20 240

20

40

60

80

100

% to

tal c

onte

nt o

f Pb(

II)

time / h

Glass cell

PS film coated glass

Adapted from J. P. Pinheiro et al., Anal. Bioanal. Chem., 2004

Pb2+(aq) Pb2+

(ads)

0.2 M Pb2+, pH 6


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Analytical Methods for Trace Metal Analysis and Speciation Analysis

3. Measurement of the analytical signal

Measuring techniques

• Atomic spectroscopy• Inductively coupled plasma-mass spectroscopy (ICP-MS)• Neutron activation analysis (NAA)• X-ray photoelectron spectroscopy• Electroanalytical methods

Separation/ extraction

• Chromatography (GC, LC, HPLC)• Capillary electrophoresis• Ion-chromatography• L-L extraction;• Ion-exchange; co-precipitation….


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IC-ICP-MS Chromatogram of 50 g/L Arsenic Species

Dimethylarsinic acid (DMA, cacodylic acid)O||

H3C-As-CH3

| OH

Arsenic acid (As+5) O||

HO-As-OH|

OH

Arsenious acid (As+3)HO-As-OH

| OH

Monomethylarsonic acid (MMA)O||

H3C-As-OH|

OH

Hyphenated techniques for speciation analysis

Separation – Excitation – Detection

HPLC – ICP – MS GC – ICP – MS IC – ICP – MS


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Metals speciation analysis by electroanalytical techniques

Free metal ion and labile formsconcentration

Free metal ion activitySample

Voltammetry

Potentiometry


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Ion-selective electrodes

Free metal ion activity, aI

IazF

RTkEMF ln

LOD: 10-7 – 10-6 M 10-11 – 10-8 M

BioavailabilitySpeciation

• Speciation of Pb(II) and Cd(II) in drinking water

• Detection of free Cu(II) in sea water

• The uptake of Cd(II) species by plant roots

Acc. E. Bakker, E. Pretsch, Trends Anal. Chem., 2005.


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Trace metal speciation analysis by voltammetry

Anodic stripping voltammetry (ASV)Adsorptive stripping voltammetry (AdSV)Potentiometric stripping analysis (PSA)

E

time

(A)

E

time

(B)

E

time

(C)

Anodic stripping voltammetry (ASV)

Voltammetric cell PotentiostatCurrent – potential curves

i - E

WE

RE

AE

00,20,4E ,V

0

-4

4

8

12

Curr

en

t, µ

A Measuredsignal

in SWASV


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How is an ASV experiment working ?How is an ASV experiment working ?

3 steps experiment:

I. Accumulation/Preconcentration (Mz+ + ze- M0(Hg))

II. Equilibration

III. Measurement of the analytical signal (M0(Hg)) Mz+ + ze-)


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Strengths and advantages of the voltammetric techniques

• Accuracy

• Sensitivity

• Simplicity

• Low detection limit (ppm - ppt)

• Well-suited for automatic in situ speciation

• Allow to determine the complexing properties of model or naturally occurring complexants


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5. Critical evaluation of the analytical performances and methods validation

To test accuracy and traceability

Use of CRM (Certified Reference Materials)

Supplier Name Material Certificate

BCR CRM 626 Solution Arsenobetaine

BCR CRM 544 Lyophilized solution Cr(III), Cr(VI)

NIST SRM 2108 Solution Cr(III)

NIST SRM 2109 Solution Cr(VI)

Example of simple certified reference materialsfor speciation analysis of arsenium and chromium in water samples

http://www.irmm.jrc.be/html/reference_materials_catalogue/catalogue/BCR/index.htm

http://www.irmm.jrc.be/html/reference_materials_catalogue/catalogue/certificates_and_reports/BCR-626_report.pdf

http://www.irmm.jrc.be/html/reference_materials_catalogue/catalogue/certificates_and_reports/BCR-626_cert.pdf

http://www.irmm.jrc.be/html/reference_materials_catalogue/catalogue/BCR/index.htm

http://www.irmm.jrc.be/html/reference_materials_catalogue/catalogue/certificates_and_reports/BCR-544_report.pdf





https://srmors.nist.gov/view_cert.cfm?srm=2108


http://ts.nist.gov/ts/htdocs/230/232/232.htm




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Acc. G. W. Luther III et al., Environ. Sci. Technol. 33 (1999) 4352

In situ detection of O2, Fe(II), Mn(II) in

sediments porewaters with

unprotected Au/Hg WE (100 μm)

Why validation methods are important?


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3.

In-situ (on-field) speciation analysis

in aquatic systems


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ATMA (Automated Trace Metal Analyzer)

VIP (Voltammetric In situ Profiler)

MPCP (Multi Physical-Chemical Profiler)In-situ voltammetric analyzers


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ATMA

• PSA measurements

• Electrodes: a mercury film deposited on a glassy carbon

rod or a thin gold electrode

• Used for measuring As(III); Cr(VI); Cu(II); Hg(II); Se(IV).

Interferences from matrix (organics, solids, other metals) can

have a dramatic effect on the accuracy of the instrument

Caution in use on unpredictable or unknown effluents

Automated Trace Metal Analyzer (ATMA)

Acc. to Space and Naval Warfare Systems Center, San Diego, USA (2002)


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In situ trace metal speciation based on bioanalogical sensors

VIP (Voltammetric In situ Profiler)MPCP (Multi Physical-Chemical Profiler)

Gel protected voltammetric microelectrodes

- GIME -Gel Integrated Microelectrode

- CGIME -Complexing Gel Integrated Microelectrode

- PLM – TAS -Permeation Liquid Membrane – Total Analytical System


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Model of metal uptake by a biological cell

Bulk solution

Diffusive boundary layer

Cell membrane

Cell interior

Cell wall layer

kint, M


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GIME (gel-integrated micro-sensor)

M MYML+ L (KML)

+ Y (KMY)

M MYML

MX

M0

Agarose gel

Ir Si3N4

Silicon

Test solution(volume)

Hg (5 μm)


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CGIME (complexing gel-integrated micro-sensor)

M MYML+ L (KML)

+ Y (KMY)

M MYML

MX

M0

M - R

Agarose gel

Si3N4

Silicon

Ir

Test solution(volume)

Resin

Hg (5 μm)


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From voltammetric sensors to in situ probes


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• Based on an array of interconnected GIMEarray of interconnected GIME sensors covered with a 300 m thick agarose antifouling gel

• Measures the concentration of dynamic fractiondynamic fraction of trace metals (Cu(II), Pb(II), Cd(II), Zn(II), Mn(II), Fe(II))

VIP – Voltammetric In situ Profiler

www.idronaut.it


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Voltammetric in situ profiler (VIP)


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Environmental monitoring and pollution control

Biogeochemical studies

Speciation of Cu, Cd, Pb Pressure pH Temperature O2

Conductivity Salinity Redox potential Turbidity Chlorophyll a

MPCP (Multi Physical-Chemical Profiler) a system for in-situ trace metal speciation

Acc. to M.-L. Tercier-Waeber/ Marine Chemistry 2005

MPCP


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MPCP – 3 channels configuration

Channel 1

GIME

Dynamic fraction of trace metals

Channel 2

CGIME

Free metal ion

Channel 3

FIA - GIME

Total extractablemetal concentration


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Speciation analysis of copper with MPCP

0

20

40

60

80

100

120

1 2 34 5 67 8 910 11

% o

f la

b to

tal c

onc.

Cu in Breakwater marine costal area (UK) at 3 different times

FIA GIME CGIME

Acc. to M.-L. Tercier-Waeber/ Marine Chemistry 2005


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Conclusions

- In situ voltammetric speciation analysis have many advantages

- It demands improvement of the voltammetric devices


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4.

Conclusions


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Interdisciplinarity and Speciation Analysis

Analytical Chemistry

Environmental Chemistry

Biology and Biochemistry

Geochemistry

•Transport processes•Consumptive processes

(chemical reactions and biological uptake)


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Summary

Analysis of trace metals in the natural environment

Speciation analysis Fractionation

Location

Laboratory In situ


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Suggestions for further reading

• R. Cornelis, J. Caruso, H. Crews, K. Heuman (Eds.), Handbook of Elemental Speciation: Techniques and Methodology, Wiley, N. Y., 2005.

• J. Buffle, G. Hoarvai (Eds.), In situ Monitoring of Aquatic Systems: Chemical Analysis and Speciation, IUPAC Ser. Anal. Phys. Chem. Environ. Syst., Vol. 6, Wiley, Chichester, UK, 2000.

• D. M. Templeton, F. Ariese, R. Cornelis, L-G. Danielsson, H. Muntau, H. P. van Leeuwen, R. Łobiński, “Guidelines for terms related to chemical speciation and fractionation of elements. Definitions, structural aspects, and methodological approaches”, Pure Appl. Chem. 72 (2000) 1453-1470.

• E. Prichard, G. M. MacKay, J. Points (Eds.), “Trace Analysis: a structured approach to obtaining reliable results”, Royal Society of Chemistry, Cambridge, 1996.

• Institute for Reference Materials and Measurements (http://www.irmm.jrc.be/html/homepage.htm)

• The European Virtual Institute for Speciation Analysis (EVISA) (http://www.speciation.net/)


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Multi pertransibunt et augebitur scientia

‘Many shall pass through and learning shall be increased’

The Great Instauration, Francis Bacon

Documents

Ana BANICA Prøveforelesning 2006 1 Analytical methods for studying trace metal speciation in the natural environment (Analytiske metoder for speciering